There is a technique called MS/MS analysis (tandem mass spectrometry) as a technique of mass spectrometry used for identification and quantitative determination of a known target component contained in a sample. The MS/MS analysis is performed using, for example, a mass spectrometer (e.g., a tandem quadrupole mass spectrometer) including a front-stage mass separator for sorting out a precursor ion, a fragmentation unit, such as a collision cell, for fragmenting the precursor ion to produce product ions, and a rear-stage mass separator for sorting out the product ions.
Multiple reaction monitoring (MRM) measurement is one of measurements in the MS/MS analysis. In the MRM measurement, mass-to-charge ratios of ions allowed to pass through the front-stage mass separator and the rear-stage mass separator are fixed, and the intensity of a specific product ion produced from a specific precursor ion is measured. The pair of the precursor ion and the product ion is called an MRM transition. In the MRM measurement, ions derived from components but not to be measured and foreign components and neutral particles that have not been ionized are removed by the two front-stage and rear-stage mass separators. Thus, it is possible to obtain an ion intensity signal with a large S/N ratio.
According to such an advantage, the MRM measurement is used for analysis of a sample containing a plurality of known target components such as a sample taken from soil or a tissue-derived sample. A chromatograph mass spectrometer combining a chromatograph (a gas chromatograph or a liquid chromatograph) with a mass spectrometer having the above configuration is used for batch analysis of such many components. A plurality of target components contained in a sample are temporally separated in a column of the chromatograph and introduced into the mass spectrometer, and the MRM measurement is performed on each of the target components.
When the chromatograph mass spectrometer executes the MRM measurement, one or more MRM measurement conditions are previously determined for each of the target components. The MRM measurement conditions include an MRM measurement time period which is a time period for executing the measurement and an MRM transition used in the measurement. Each MRM measurement time period is determined so that the MRM measurement time period includes the chromatographic retention time of the target component to be measured, and the MRM transition is determined with reference to database. A set of one or more MRM measurements performed for one target component is called an event. Each of the MRM measurements is called a channel.
In a batch analysis of a plurality of components, the plurality of MRM measurement time periods often overlap each other partially or entirely. In such a case, an operation for sequentially executing the plurality of channels set in the overlapping time period one by one for a predetermined time is repeatedly performed. The execution time for executing each channel once is called a dwell time, and a total time required for executing the plurality of channels once in the same time period is called a loop time. When the batch analysis of the plurality of components is planned, for example, a user sets an appropriate loop time, and the set loop time is divided by the number of channels executed in the same time period to determine a dwell time.
A mass chromatogram corresponding to each channel is obtained by executing the measurement of the sample under the MRM measurement conditions determined as described above. Normally, in an MRM measurement, an MRM transition with which target components can be measured with the highest sensitivity (that is, having the highest efficiency of producing product ions) is selected. However, the sensitivity differs between target components. Thus, when an equal dwell time is allotted to each channel, a peak intensity may be too small in a mass chromatogram obtained in some channels to perform quantitative determination.
Thus, in a conventional technique, a user checks a mass chromatogram acquired in each channel, and extends the dwell time of a channel having a small mass peak intensity in order to create adequate MRM measurement conditions under which target components can be measured with high sensitivity in all channels.